Optical modulator and optical module using this

An optical modulator has an optical modulation element including optical waveguides and a housing that accommodates the optical modulation element. The housing has a bottom surface wall having a quadrilateral shape in a plan view, first and second long side walls that are connected to two opposite edges of the bottom surface wall, and first and second short side walls, shorter than the long side walls, and connected to two other opposite edges of the bottom surface wall. The optical modulation element is accommodated in a space surrounded by the bottom surface wall and the side walls. The second long side wall has a wall thickness that is equal to or larger than that of the first long side wall, and at least one of the first and second short side walls has a wall thickness that is thinner than that of the first long side wall.